The genesis of dental caries is a complicated process, involving bacterial adhesion to pellicle, accumulation of bacteria, foodstuffs and salivary proteins to form plaque, and finally the production of organic acids by the bacteria. The localized production of acid may result in the localized demineralization of the tooth. Interference in bacterial adhesion, accumulation or acid production may prevent caries formation. The mutans streptococci are the pripiary causative agents of dental caries. These bacteria are acidogenic and aciduric. The mutans streptococci can also utilize sucrose as a source of fermentable carbohydrate and as a substrate for D-glucan synthesis. The D-glucans may be involved in the sucrose-dependent accumulation of streptococci on pellicle. It is a thesis of this proposed research that the streptococcal glucan-binding lectin (GBL) is a virulence coniponent. The lectin may tether streptococci to glucan on pellicle or the lectin may serve to anchor streptococci to streptococci in plaque. We are now in a position to study the structure, function, regulation and role in caries of the GBL of the mutans streptococci. The specific aims for this research are outlined below. 1) To purify and characterize the GBL from S. sobrinus and other selected oral streptococci. 2) To study the inhibition of the GBL by fluoride and chelating agents, including lactic acid. 3) To study how manganous ion regulates GBL activity in S. sobrinus and other oral streptococci . 4) To determine if sucrose induce-s GBL activity in S. mutans and other oral streptococci. 5) Synthesize glucan and chemically-modified glucan inhibitors of GBL. 6) Clone the GBL gene fron, Streptococcus sobrinus 6715 into the GBL-free Streptococcus mutans GS-5. 7) Study caries induction rats employing S. mutans GS-5 GBL- and S. mutans gbl+'. Determine whether glucan T-10 or its derivatives will inhibit caries induced by sucrose in rats infected with either S. sobrinus 6715 or S. mutans gbl-'. These studies will reveal important new information about the role of the streptococcal GBL in dental caries.